Discussion LKS inspired shuttle concept.

[Urwumpe]

In case of abort the spaceplane is supposed to fly away with its own engines? Or will have some sort of LES, maybe small detachable SRB at the flanks of the fuselage? Or nothing at all?

Does it need something at all? A pad abort or early ascent abort will be likely impossible, because of the low speed and altitude. You simply can't add enough impulse to the spaceplane to glide to a safe landing after an abort there. And you also need a lot of thrust there, which would make the engines inaccurate for orbital maneuvers.

The only halfway sane criticism I have right now is, that I would like to see a stack configuration that follows the area rule for reduced drag during max Q.

And of course, will it have radiators?

 

[K_Jameson]

Every manned spacecraft needs some sort of escape system, unless you rely entirely on the total reliability of the system, as STS did... matter of choices...

And yes, as seen, this spaceplane hardly support a LES, because it hasn't an ejectable cabine, it can't glide to home in case of an abort a zero or low altitude/velocity and, lastly, the in-built engines probably will not have the thrust for a propulsive abort (but I asked).

My thinking was about contingency parachutes deployed after a propulsive abort with expendable SRB's laterally-mounted, as in the Grumman proposal for STS. The problem is that the spaceplane could be destroyed by aerodynamic forces in case of an high velocity abort.

 

[Urwumpe]

Every manned spacecraft needs some sort of escape system, unless you rely entirely on the total reliability of the system, as STS did... matter of choices...

Even Apollo did not have a full abort envelope (= it is always possible to abort the mission), it did not even have such a feature during ascent.

Despite the pad abort possibility, various constraints limited the use of the LES during early ascent, like exceeding dynamic pressure constraints or too low separation from the booster.

Yes, you don't need to go to such extremes as the Shuttle, but it is a lot harder to abort with a space plane. If you add an LES that allows pad aborts and aborts in the first 55 seconds, you effectively double the payload weight. If you can't discard the LES early, the penalty accumulates until it also reduces the payload to orbit. For the Shuttle for example, it would have been just enough already to provide large sump tanks for LH2 and LOX in the aft body of the Shuttle, so the main engines can run for a few seconds after ET separation. But if you calculate the needed volume and mass for such a solution, including the need for a more or less safe shutdown of the SSMEs, it again becomes very unattractive. Especially since this only works for aborts triggered by a subsystem, that is then not needed for the abort - which is just ET and SRBs. An SSME failure would made it impossible to abort.

 

[Lmoy]

Even Apollo did not have a full abort envelope (= it is always possible to abort the mission), it did not even have such a feature during ascent.

Despite the pad abort possibility, various constraints limited the use of the LES during early ascent, like exceeding dynamic pressure constraints or too low separation from the booster.

Yes, you don't need to go to such extremes as the Shuttle, but it is a lot harder to abort with a space plane. If you add an LES that allows pad aborts and aborts in the first 55 seconds, you effectively double the payload weight. If you can't discard the LES early, the penalty accumulates until it also reduces the payload to orbit. For the Shuttle for example, it would have been just enough already to provide large sump tanks for LH2 and LOX in the aft body of the Shuttle, so the main engines can run for a few seconds after ET separation. But if you calculate the needed volume and mass for such a solution, including the need for a more or less safe shutdown of the SSMEs, it again becomes very unattractive. Especially since this only works for aborts triggered by a subsystem, that is then not needed for the abort - which is just ET and SRBs. An SSME failure would made it impossible to abort.

What kind of LES would be optimal for this shuttle, in your opinion? Would an Eridanus-style LES work, or would it be too dangerous during max Q, or incur too much of a weight penalty in general?

 

[Urwumpe]

What kind of LES would be optimal for this shuttle, in your opinion? Would an Eridanus-style LES work, or would it be too dangerous during max Q, or incur too much of a weight penalty in general?

MaxQ would be a problem, but I also see some trouble there with the direction in which it fires - it does not quickly separate from the rest of the launcher, but launches straight up in the first seconds. So, even normal aerodynamic forces would rather pull it towards the stage first (similar problem as dropping bombs from a fast aircraft, which is solved by huge pyrotechnic forces in the bomb pylon), instead of away. And gusts and high attitude rates would also be a problem.

Then, it is of course a bit bad to mount a LES at the place where any penetrations of the heat shield are rather annoying. Also you need structural reinforcements for taking the pulling loads (which are worse than compressions), which make the nose pretty heavy even after separation.

But hey, Orbiter is not reality. Colliding with the stage during abort looks bad but is not THAT bad, and structural weaknesses are not that much important.

The primary problem that you have to solve is vertical separation in the first milliseconds of abort. Pneumatic pushers could contribute to it (Like ejection seats use), but finally you need turn pitch away from the core stage fast even before you have full acceleration.

Thruster modules at the sides of the spaceplane could help there, structural reinforcements would also not be needed that much and getting vertical separation would be easier by using extra pushing thrusters, but again, they would need to be pretty heavy to allow a good abort.

It is a very tough problem, since you essentially want to do something with a spaceplane, that counters the usual requirements on a spaceplane. You have forces at places and in directions, you usually don't have. You need to fly out of a place, that you can only leave with violent force at high dynamic pressures.

Any solution has its disadvantages and will never be perfect. A smaller plane could likely abort easier than a 125 ton Space Shuttle. But it would still mean loss of performance.

 

[K_Jameson]

Would an Eridanus-style LES work, or would it be too dangerous during max Q, or incur too much of a weight penalty in general?

I don't see why it should not work, if you consider Eridanus cabin as a capsule's command module. In fact, it is only marginally larger than Antares CM.

 

[Lmoy]

So it's really up to the project's design/engineering team what level of risk they're willing to take versus how much weight they're willing to sacrifice. Makes sense!

By the way Loru, the whole vehicle is looking really nice now. I like what you've done with the boosters!

 

[Urwumpe]

So it's really up to the project's design/engineering team what level of risk they're willing to take versus how much weight they're willing to sacrifice. Makes sense!

Yes. And also of course, in which phase of the mission they plan to take risks. Perfect solutions only happen in perfect worlds.

 

[ISProgram]

I'm more concerned about how the shuttle will handle any abnormal loads in a abort.

 

[K_Jameson]

What kind of LES would be optimal for this shuttle

My two cents on a "pusher" LES in in the manner of the Grumman proposal I linked above. Anyway, the orbiter seems relatively large for any LES. An adequate LES for that mass would lead to an unacceptable weight penality and the spaceplane itself could break apart in an abort event because seems large and thus proportionally "fragile". No way for gliding back to home: an additional contingency system, to be used after the abort maneuvre, must be integrated (parachutes? Ejectable seats?). This would lead to even more weight penalities. The current launcher would be heavily insufficient.

An even smaller spaceplane, mounted on top, and with LES integrated on the rocket adapter would be a decent solution. This is the way that we followed during the development of our Delphinus mini-spaceplane. I don't say that was better, but at that time it looked good. Take in account that Delphinus weight is less than one half of this, and the launcher used (Jarvis S) had a very large margin that was allocated to a correctly sized LES, complete with a fairing that in our intention would protect the spaceplane from abnormal aerodynamic loads during the abort. Our task was easier.
Oh, and Delphunus is equipped with contingency parachutes and inflatables for splashdown because we assumed that after an abort it will be ungovernable and/or the space and velocity would be insufficient for gliding at home. The LES is "zero-zero" and can take away the spacecraft even with the rocket still on ramp. But again, Delphinus is tiny in respect to this. With a 25-ton spaceplane everything is more complicated...



---------- Post added at 06:35 PM ---------- Previous post was at 05:51 PM ----------

Even Apollo did not have a full abort envelope (= it is always possible to abort the mission), it did not even have such a feature during ascent.

Despite the pad abort possibility, various constraints limited the use of the LES during early ascent, like exceeding dynamic pressure constraints or too low separation from the booster.

Yes, you don't need to go to such extremes as the Shuttle, but it is a lot harder to abort with a space plane. If you add an LES that allows pad aborts and aborts in the first 55 seconds, you effectively double the payload weight. If you can't discard the LES early, the penalty accumulates until it also reduces the payload to orbit. For the Shuttle for example, it would have been just enough already to provide large sump tanks for LH2 and LOX in the aft body of the Shuttle, so the main engines can run for a few seconds after ET separation. But if you calculate the needed volume and mass for such a solution, including the need for a more or less safe shutdown of the SSMEs, it again becomes very unattractive. Especially since this only works for aborts triggered by a subsystem, that is then not needed for the abort - which is just ET and SRBs. An SSME failure would made it impossible to abort.

I agree with you.
My thinking is simple: if, for a given task, I can chose between a design that offers no abort possibilities and a design that offers even just limited abort possibilities, I go for the last one. For a mere crew transport to and from LEO, I go for a capsule (or a very minimal spaceplane with abort capability). Sure, Orbiter is not reality and a large spaceplane is cooler :lol: :thumbup:

 

[Loru]

To answer some of your questions:

In case of abort the spaceplane is supposed to fly away with its own engines? Or will have some sort of LES, maybe small detachable SRB at the flanks of the fuselage? Or nothing at all?

Shuttle engines won't have enough umph to get craft to safety quickly enough. In this case however I can alway shut down the engines and then detach the shuttle - that's advantage of liquid or hybrid engines.

I'll investigate SRB powered LES though. All I need is around 5 seconds of thrust with 6g acceleration. Maybe some form of "kick stage" attached to the end of the shuttle with 3 solid motors firing in sequence for final insertion and fired all at once for LES duty. That way I won't waste lots of dV for things used only in abort.

To be determined...

...And of course, will it have radiators?

Yes. There is dorsal APAS compatibile docking port so inner surface of door will be covered in them. Not modelled yet though. Also I have some room in rear section so I may actually model some sliding out pair (think CD tray)

 

[Lmoy]

To answer some of your questions:
I'll investigate SRB powered LES though. All I need is around 5 seconds of thrust with 6g acceleration. Maybe some form of "kick stage" attached to the end of the shuttle with 3 solid motors firing in sequence for final insertion and fired all at once for LES duty. That way I won't waste lots of dV for things used only in abort.

So the LES will be used as part of normal insertion when things go correctly? That sounds like a pretty good idea. Has it ever been done before?

 

[K_Jameson]

An integrated LES/main engine is part of the Dream Chaser project and, if I recall correctly, of the CST-100/Starliner and Dragon 2.

Loru's idea appears very clever. Looking forward for some graphical interpretation...

 

[Pipcard]

I am not sure how Dream Chaser would have been able to use the same engines for abort and as an orbital maneuvering system, that's a very deep throttle range.

The big engines of CST-100 (Starliner) will only be used for abort. The Superdracos of Dragon V2 will only be used for abort and propulsive landing; the minimum throttle percentage is 20%.

My Reusable Crew Vehicle add-on was supposed to do the same thing as what Dream Chaser would do (abort functionality hadn't been put in the add-on, but in-universe it's supposed to be there). The thrust in orbit was set to be 5% of a 6-g abort. I should have had on-orbit operations only use RCS thrusters, but then people might have been confused as to why the bigger engines weren't functional.

 

[Loru]

I've done some calculations however in order to keep 6G for ~5 seconds I need 3 ton system with 1.6 MN thrust. Yes. I can imagine splitting into for example 4 or even 8 separate engines however I'm not sure solids are precise enough for the final insertion burn.

I may sacrifice 4-5 tons for LES duty anyway. Need more study though.

Maybe I'll stick this LES on shuttle and drop it shortly after booster separation

 

[K_Jameson]

Seems that such a LES is not conceived to manage a failure as the Orbital Taurus II (i call it "Taurus II" instead "Antares" because Antares is [ame=http://www.orbithangar.com/searchid.php?ID=4682]OURS![/ame] ;-))

Seems reasonable, because such a spaceplane unlikely can survive a classical high acceleration escape (in the range of 15 G) in one piece. And it lacks a parachute or something...

---------- Post added at 09:27 AM ---------- Previous post was at 09:25 AM ----------

I'm not sure solids are precise enough for the final insertion burn.

This is also my concern; probably it can enough for a rough parking orbit that must be corrected with the orbiter's OMS.

 

[Urwumpe]

This is also my concern; probably it can enough for a rough parking orbit that must be corrected with the orbiter's OMS.

Yes, but it means you need a higher propellant mass in the spaceplane, because you have to calculate with a higher dv budget for orbit insertion. Also, such things like a 4-orbit docking approach would be impossible then.

 

[K_Jameson]

Yes, but it means you need a higher propellant mass in the spaceplane

And, in turn, an higher propellant mass in the LES/kick stage to achieve the desired performances.

 

[Urwumpe]

And, in turn, an higher propellant mass in the LES/kick stage to achieve the desired performances.

Yes. luckily, this differential equation does eventually converge. :lol:

 

[fred18]

Could the solids be used during ascent together with the other engines like oms assist of the sts? In this way the cutoff precision will be achieved by regular engines